1. Field of the Invention
The present invention relates generally to resilient pads, mattresses, and the like for supporting the human body and more particularly is directed to pads or mattresses made of foamed material and constructed so as to more evenly distribute the pressure on a body resting thereon than would be the case with a solid slab of foam material, with the object of minimizing pressure on the skin to avoid injury and in particular to prevent formation of decubitus ulcers, also known as bed sores.
2. Background of the Invention
A great deal of effort has been expended in the past in efforts to devise and improve mattresses and pads of various types so as to distribute as evenly as possible the pressure exerted on the body of a person resting theron. Given the irregular shape and weight distribution of the human body, when a person is laid down or sits upon a plane surface, however resilient that surface may be, there are areas of the body in contact with the supporting pad surface which will carry a disproportionate pressure load. In a bed-ridden person resting supine on a horizontal, uniform surface, areas of high local pressure are typically found at the back of the heels, the sacrum area, and the back of the head. In a side position, areas of peak pressure are typically found in the hip bone or trochanter area in contact with the supporting surface.
Protracted pressure against any portion of the skin has the effect of diminishing or cutting off peripheral vascular flow to that area. If impairment of blood flow to the affected area is sufficiently prolonged, the tissues underlying the affected skin area will be starved of nutrients and suffer progressive damage. Typically it is the underlying soft tissues which are first damaged, until eventually the skin undergoes necrosis and ulcerates in progressive manner, and unless the pressure on the area is removed, such ulcers can become deep open wounds which are difficult to treat and slow to heal.
Numerous advances and improvements have been made in the past to overcome this problem. One approach to resolving this difficulty has been to design and construct foamed material mattresses and pads which are modified so as to take into account and accommodate the areas of the body at which high pressure levels are typically encountered.
Towards this end, it is known in the prior art to provide foam pads and mattresses which are slit, cut or scored so as to modify the tensile force of the foam material at different locations across the supporting surface of the pad. Examples of this approach are disclosed in U.S. Pat. Nos. 3,828,378 to Flam and 4,110,881 to Thompson. Both of these prior patents disclose foam mattresses having a rectangular body supporting surface which is selectively cut to select depth in a rectangular grid pattern over particular areas of the supporting surface. The gridded score lines define individual columnar elements or blocks which are attached at their bottom to an uncut, interconnecting bottom layer of the pad thickness, typically contiguous to the under surface of the pad. These individual blocks are more easily compressible than an even, unscored supporting surface because the score lines have the effect of eliminating lateral tensile forces which normally act within an unscored pad when a point pressure is applied to its surface. The compressibility of such an uncut pad is a function of a combination of the vertical compressibility and the lateral tension in the foam material which tends to resist local compression of the material. The improved local compressibility of the individual blocks, for a given resilient pad material, is a function of the depth of cutting or scoring, i.e. vertical height of the individual block, and of the surface area of the individual blocks. Compressibility increases with depth of cut and is an inverse function of the block surface area. Consequently, as described in the cited prior art patents, variations in firmness or compliance across the supporting surface of the foam pad may be achieved by scoring at least a portion of the pad surface and varying either or both the depth of scoring and the spacing between score lines in selected regions of the pad surface. The regions are normally selected so as to achieve a complementary relationship between pad compliance and pressure on particular areas of the body supported by the pad. Thus, it is appropriate to provide more compliant supporting regions underlying the head, hip or saccrum, and the feet and heel supporting portions of the foam pad. As described in the cited Flam reference, a pad can be rather closely tailored to empirically obtained body pressure curves so as to optimize weight distribution on the pad surface and thereby minimize pressure applied to any given portion of the patient's body.